Go to Section
A-B-C-D-E-F-G-H-I-J-K-L-M-N-O-P-Q-R-S-T-U-V-W-X-Y-Z
- B cell
- A lymphocyte that synthesizes antibodies. Antibody-secreting cells, called plasma cells, are derived from B cells. [Discussion] [interaction with helper T cells] [how antibody diversity is generated]
- Bacillus thuringiensis
- Discussion
- Bacteriophage
- Virus that infects bacteria.
- Balanced polymorphism
- The maintenance of two or more distinct phenotypes in a population by natural selection. Balanced polymorphism can occur as a result of disruptive selection or if (as in sickle-cell anemia) the heterozygotes are more fit than either homozygote.
- Barbiturate
- Any of the derivatives of barbituric acid used as sedatives (e.g., phenobarbital) [More]
- Barr body
- Defined
- Base
- Molecule or ion that can take a proton from an acid. [Discussion]
- Base pairing
- [DNA]
- Basidium
- Club-shaped spore-producing structure of basidiomycetes on which four basidiospores are formed.
- Basophil
- BCL-2
- Proto-oncogene associated with B-cell leukemia/lymphoma. [Discussion] [Role in apoptosis]
- bcr
- [oncogene]
- BCR
- B-cell receptor for antigen [Discussion] [how its diversity is generated]
- Benzodiazepines
- a class of tranquilizer
- Beta conformation
- [Protein]
- Beta-galactosidase
- An enzyme (e.g., "lactase") that hydrolyzes the disaccharide lactose and related molecules. [synthesis by Z gene of lac operon]
- Beta-2 microglobulin
- subunit of class I histocompatibility molecules
- bicoid (bcd)
- Drosophila selector gene.[see encoded homeodomain] [in segmentation] [role in forming the head]
- Bile acids
- [from cholesterol]
- Bioassay
- Quantitative determination of the concentration of a biologically active substance from its effect on a living tissue.
- Biochemical oxygen demand (BOD)
- The oxygen needed (in milligrams per liter or parts per million) by bacteria and other microorganisms to oxidize the organic matter present in a water sample such as water polluted by sewage. The BOD of drinking water should be less than 1. That of raw sewage may run to several hundred. Also called the biological oxygen demand.
- Biomass
- The total amount of living matter in a given population or community.
- Biome
- A large distinctive complex of plant communities created and maintained by climate. The coniferous forest region of North America constitutes a single biome (the taiga).
- Biosphere
- The part of our planet in which life exists and with which it exchanges materials. Includes a small part of the lithosphere (the solid earth) and large parts of the hydrosphere (water) and atmosphere.
- Bipolar cells
- of human retina
- Bivalent
- Two homologous chromosomes held together by chiasmata prior to anaphase I of meiosis. A bivalent contains four chromatids and for this reason is often called a tetrad.
- Blastocyst
- The blastula formed by placental mammals. The blastocyst is the embryonic stage that implants in the wall of the uterus. [human]
- Blastula
- Early stage of animal development in which a single (usually) layer of cells surrounds a fluid-filled cavity (the blastocoel), thus forming a hollow ball. [frog]
- Blind spot
- on human retina
- Blood
- [general discussion] [blood groups] [blood pressure]
- Blood-brain barrier
- Bond energy
- Bonds
- [covalent]
[ionic]
[polar covalent] [noncovalent]
- Bone Morphogenetic Proteins (BMPs)
- [in embryonic development]
- Botany
- The study of plants.
- Brain, human
- Branchial grooves
- Series of external, paired grooves in the neck region of vertebrate embryos that correspond in position to the outpocketings of the pharynx (the gill pouches).
- Bryophyta
- Bt
- Bacillus thuringiensis. [More]
- Budding
- Asexual reproduction in which a new organism develops from an outgrowth of a single parent.
- Burkitt's lymphoma
- [Discussion]